This application claims the priority of 198 18 864.1, filed Apr. 28, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a selection system for an automatic motor vehicle transmission and more particularly, to a selection section having a manual selector element arranged to be manually adjusted to different positions for selecting transmission adjustments, and a locking device having a controllable actuator arrangement for automatic locking and unlocking of the selector element in at least one defined position as a function of defined operating conditions.
The invention relates to all types of automatic transmissions, particularly, fully automatic and partially automatic gear boxes. In addition, so-called automatic converter step mechanisms and variable transmissions with infinitely variable transmission ratios with or without gears are also contemplated.
In vehicles with automatic transmissions, a selector element, usually a selector lever, is provided for selecting a desired transmission adjustment. The selector lever can be adjusted to different positions, such as a parking position P, a reversing position R, a neutral position or engine idling position N, a normal forward driving position D with an automatically variable transmission ratio and optionally also one or several forward driving positions with an invariable transmission ratio.
The known selector lever is combined with a so-called shiftlock function, via which the release of the selector lever from the parking position P is possible only when certain operating conditions are fulfilled, e.g., when the ignition key of the vehicle has been operated in the ignition lock (for example, the ignition was switched on) and the brake pedal is also depressed. It happens frequently in normal operation that, although the ignition is initiated, the driver forgets to depress the braking pedal so that a manual operating force is exercised on the selector lever, while the selector lever is still locked in the parking position P.
In a selection system, as described, for example, in DE-196 41 706 C1, when the brake is operated only subsequently, a solenoid can no longer release the lock for the following reasons. The manual force entered by the driver into the selection system is transmitted to a cam disk. The cam disk is held by a locking lever in a locking contour of the cam disk in the parking position P as long as, by way of a solenoid, an auxiliary force is not transmitted to the lever such that the locked engagement of the locking lever on the locking contour is released.
Because of the mechanical connection of the elements, the releasing force is proportional to the manual force on the selector lever. Consequently, starting from a defined manual force, the solenoid will no longer be strong enough to overcome the locking forces, particularly the frictional forces generated by the manual force and to release the engagement of the locking lever in the locking contour. This condition will exist when the manual introduction of force takes place at the selector lever before the ignition key has been operated and/or before the brake is operated. The brake must be operated before and while a manual force is exercised on the selector lever.
Although changes of the limit value of the release force between the locking lever and the locking cam are possible in small amounts, the locking kinematics and the capacity of the solenoid are restricted to space-related parameters. Because of the limited space and also because the heat generates, the solenoid cannot be arbitrarily enlarged. A further locking contour in the cam disk, forms a second lock in combination with the locking lever. As a function of the driving speed in the forward drive, a manual engagement of the reverse gear is prevented as long as the driving speed is above a defined limit value of, for example, 8 km/h. The locking lever is loaded by spring devices in a direction opposed to the solenoid and, when the solenoid is switched off, is moved back into the opposite direction.
EP 0 709 597 A1 describes a selection system which has a locking arrangement in which a toggle lever operated by a solenoid blocks the manual operation of the locking element in the extended position.